MOLDING MATERIAL

Abstract

The present invention relates to a molding material comprising: a) a primary nonwoven fiber layer; b) a secondary nonwoven fiber layer; and c) a resin layer; wherein the resin layer bonds the secondary nonwoven fiber layer to a first surface of the primary nonwoven fiber layer, and the resin layer is exposed on the second surface of the primary nonwoven layer.

Description

MOLDING MATERIAL The present invention relates to a molding material, in particular but not exclusively to a molding material for surface applications. Background of the invention The present invention relates to molding materials that provide an improved surface finish, the use of the molding materials in combination with one or more layers of pre-impregnated fibrous reinforcement to form a laminated structure, the use of the molding materials in combination with dry (non-impregnated) fiber layers to form a laminated structure, and a method of forming laminated structures using the molding materials. The present invention relates particularly to fiber-reinforced composite molding materials that can be cured at low temperatures and include a surface finish layer to provide a molded article with a high-quality surface finish requiring minimal preparation after curing, especially, but not exclusively, for use in the wind turbine and automotive industries. Composite materials have well-documented advantages over traditional construction materials, particularly in providing excellent mechanical properties at very low material densities. As a result, the use of such composite materials has become widespread in many industries, including aerospace, automotive, marine, and wind turbine. Prepregs, comprising a fiber array impregnated with a thermoset resin, such as epoxy resin, are widely used in the production of such composite materials. Typically, a series of layers of such prepregs are applied as desired, and the resulting assembly, or laminate, is placed in a mold and cured, usually by exposure to elevated temperatures, optionally under pressure, to produce a cured composite laminate. In an alternative manufacturing technique, a fibrous material is placed, usually within a shell, into which a liquid resin system can be infused to envelop the fibrous material, where it can then be cured to produce the finished article. The shell may be completely enclosed around the fibrous material, and the resin is introduced under vacuum (occasionally known as the vacuum chamber technique).Alternatively, the shell can be a mold, and the resin can be injected into the mold (occasionally known as resin transfer molding), which can also be vacuum-assisted (known as vacuum-assisted resin transfer molding). As with the system described above in relation to prepregs, the liquid resin system can be an epoxy resin, a cyanate ester resin, or a bismaleimide resin, and will also contain a curing agent for the particular resin. However, without any surface treatment, composite materials produced by any of the above techniques often cure to a poor surface finish, which can manifest as a rough, wavy, or pitted surface, or as narrow grooves on the surface of a molded structure where adjacent layers of prepregs have been overlapped to ensure a continuous layer. This tendency to form an uneven surface appears to be closely related to the roughness of the underlying reinforcement; the problem is more pronounced the rougher the reinforcement. This can be a particular problem when rough reinforcement is used for structural stiffness, yet a smooth surface finish is desirable, such as in the production of automotive body panels, where a Class A finish is required, or in the production of wind turbine blades. Document GB2445929 discloses a fiber-reinforced composite material mold comprising a surface portion laminated to a structural portion. The surface portion is formed by a surface layer comprising a plurality of surface layer segments molded together to form a continuous surface layer. The surface layer comprises a first cured resin material supported on a sheet material backing. The structural portion is formed from at least one layer of fibrous reinforcing material and a second cured resin material. At least one layer of the fibrous reinforcing material is formed by a plurality of segments, each of which covers a respective surface layer segment, and each surface layer segment overlaps an adjacent segment of the fibrous reinforcing material. We have found that this molding still has an inferior surface quality, as the impression of the underlying carrier material and the fibrous reinforcement material is evident. Furthermore, the layering requires overlaps, which in turn result in surface defects in the form of visible seam lines. WO2008 / 007094, shown in Figure 2, discloses a surface material comprising a resin layer, a veil, and a fleece layer. The resin layer is in contact with a mold surface, and the veil adheres to it. The fleece contains resin strips that facilitate the adhesion of the fleece layer to the veil, leaving the fleece layer only partially impregnated with resin. This material suffers from the problem that the resin content of the surface layers is low, requiring any subsequent prepreg layer to have a higher resin content. This means that prepreg materials with a significantly higher resin content than usual (typically over 60% by weight) can only be used in combination with this surface material, which is complicated, inefficient, and expensive.Furthermore, the manufacture of the fleece layer with resin strips is complicated and therefore inefficient and expensive, since conventional reinforcing layers are impregnated across their entire surface. WO 2017 / 021147, shown in Figure 2, discloses a surface material comprising a surface layer consisting of a resin layer sandwiched between a veil and a fleece layer. The veil layer is in contact with a mold surface, and the veil and fleece layers adhere to the resin layer, leaving the veil and fleece layers largely unimpregnated. This facilitates the release of any air trapped in the layering near the mold surface. However, this material still suffers from the problem of low resin content in the surface layers, necessitating that any subsequent prepreg layer have a higher resin content, which is complicated, inefficient, and costly. The present invention aims to prevent or at least mitigate the problems described above and / or provide improvements in general. Brief description of the invention According to the invention, a molding material, preferably a surface material, uses of the molding material, and a method of manufacturing a laminated structure as defined in any of the appended claims are provided. The present invention provides a molding material comprising: a) a primary layer of non-woven fiber; b) a secondary layer of non-woven fiber; and c) a layer of resin; where the resin layer bonds the secondary nonwoven fiber layer to a first surface of the primary nonwoven fiber layer, and the resin layer is exposed on the second surface of the primary nonwoven layer. Surprisingly, we have now found that having an exposed resin layer on the surface of the molding material of the present invention, in combination with layers of non-woven fiber, provides excellent surface quality without speckling. We have also discovered that the occurrence of cosmetic defects due to printing through carbon fiber reinforcement layers is prevented by the configuration of the molding material of the present invention. The materials of the present invention also provide an excellent surface finish when used as a mold or tool contact layer when preparing laminated products employing pre-impregnated reinforcing materials and / or non-impregnated reinforcing materials in pre-impregnating or infusion systems. Furthermore, we have discovered that pre-impregnated reinforcing layers with a resin content of between 30% and 45% by weight of the prepreg can be used with this material without any adverse effect on the cosmetic quality of the surface. This allows the use of standard prepreg materials in combination with this molding material, thus avoiding the need for a higher resin content. In one particular aspect of the present invention, the molding materials of the invention can be provided as a surface finish layer, i.e., without reinforcing layers, whereby in this aspect the molding materials can essentially consist of the primary nonwoven fiber layer, the secondary nonwoven fiber layer, and the resin layer. In an alternative aspect, the molding materials can be provided as a reinforced surface finish layer, and in this aspect the molding material can comprise a reinforcing layer, with the secondary nonwoven layer located between the primary nonwoven fiber layer and the reinforcing layer. ηζηαηη / ζζηζ / Ε / γίΛΐ Specific description The specific embodiments of the invention will now be described in more detail and by way of example as follows. In the molding materials of the present invention, the resin layer bonds the secondary nonwoven fiber layer to a first surface of the primary nonwoven fiber layer, and the resin layer is exposed on the second surface of the primary nonwoven layer, and, therefore, the primary nonwoven fiber layer will generally be completely saturated by the resin layer. Furthermore, in certain embodiments, the secondary nonwoven fiber layer is at least partially impregnated, and optionally completely impregnated, with the resin from the resin layer. In particular, in the embodiments of the present invention, the resin layer comprises a formulated resin matrix comprising at least one resin component, at least one curing agent, and optionally, a filler. The formulated resin matrix forming the resin layer may comprise a thermoset resin, such as a polyester resin, polyurethane resin, polyurethane / polyurea resin, phenol-formaldehyde resin, urea-formaldehyde resin, vinyl ester resin, cyanate ester resin, polyimide resin, or epoxy resin. Unlike thermoplastic resins, thermoset resins harden irreversibly upon curing, so any molded article produced from them is resistant to deformation. In one embodiment, the first resin composition is a thermoset resin composition, preferably an epoxy resin composition, i.e., comprising an epoxy resin or a mixture of epoxy resins. The resin layer preferably comprises at least one multifunctional bisphenol epoxy resin material in combination with a urea-based curing agent. A preferred formulated resin matrix for this layer is M79 resin supplied by Hexcel Corporation. In another embodiment of the invention, the formulated resin matrix comprises between 1 wt% and 10 wt% of a filler based on the weight of the formulated resin matrix, preferably a silica filler or an organophilic phyllosilicate, preferably a pyrogenic silica filler with a compacted density of 60 g / L. A preferred filler is Aerosil R202 supplied by Evonik Industries. We have discovered that the inclusion of a filler reduces the flow of the resin layer, which is beneficial in layering involving substantial vertical surfaces, such as in the manufacture of boat and yacht hulls. The primary and secondary nonwoven fiber layers of the present invention preferably have the following properties and characteristics. The nonwoven fiber layers may contain any nonwoven material that is permeable to air and resin. Suitable nonwoven fiber backings are lightweight, preferably less than 100 g / m², but are preferably robust enough to carry a resin layer and withstand handling during layering and processing to form composite parts that have a high-quality cosmetic surface. The non-woven fiber layer may comprise continuous or discontinuous fibers. In one embodiment, the primary nonwoven layer comprises a veil. In the context of the present invention, the term veil refers to a thin, lightweight (i.e., a weight per unit area of ​​no more than 100 g / m2), porous, nonwoven, woven, or fibrous reinforcement. In preferred embodiments, the primary nonwoven layer commonly consists of nonwoven fibers of a thermoplastic material, preferably where the fibers are bonded together using an organic binder to impart structural integrity to the material. In one particular embodiment, the thermoplastic material comprises a polyester, a polyamide, preferably an aliphatic or semiaromatic polyamide, and / or a combination of a polyester and a polyamide. The organic binder, where present, is generally present in an amount of between 1% and 10% by weight based on the total weight of the primary nonwoven layer. The purpose of the primary non-woven layer is to act as a support or backing for the resin layer, retain the resin on the outer surface, and control the way in which the resin interacts with the surface of a mold or tool to provide a good surface finish. In one embodiment, the primary nonwoven material has an opening of between 1% and 10%, preferably between 2% and 89%, and / or an average open area of ​​between 75 pm2 and 350 pm2. In later embodiments, the primary nonwoven fiber layer has a weight per unit area in the range of 1 g / m2 and 80 g / m2, preferably between 5 g / m2 and 50 g / m2, more preferably between 15 g / m2 and 40 g / m2. In one embodiment, the primary nonwoven fiber layer has an air permeability of approximately 2300 L / m² / s at an applied pressure of 200 Pa (measured in accordance with ASTM D73718). Suitable thermoplastic fiber material in veil form that can be used as the primary nonwoven fiber layer includes those commercially available under the trade name Optiveil® from Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, UK, as Optiveil T2761-00. Aperture measurements can be performed using a Keyence VHX-6000 series digital microscope manufactured by Keyence (UK) Limited, Milton Keynes, Buckinghamshire, UK. The non-woven material can be presented to the microscope mounted on a blue plastic card to help highlight the open areas when viewed on the computer monitor. The microscope is set to 175x magnification with the light output set to maximum and the gain selector adjusted so that the open areas can be clearly identified. The saved computer image represents a total area of ​​2951002 pm². The Keyence software is used to measure the average open area (i.e., the empty space between fibers) and the percentage of openness. The image is also manipulated by adjusting sliders on a histogram to create a two-color image where one color represents the fibers and the other represents the open space. The software is used to measure the areas of all individual open spaces. This data can be saved to a spreadsheet and used to calculate the total area occupied by open spaces (to calculate the percentage of openness) along with the average size of the open areas. The secondary nonwoven fiber layer may comprise a nonwoven fiber material containing continuous or staple fibers. The secondary nonwoven fiber material may comprise nonwoven fibers of glass, carbon, polyester, polyamide, aramid (aromatic polyamide), or combinations thereof, optionally bonded by an organic binder to impart structural integrity to the material. Preferably, the secondary nonwoven fiber layer comprises a glass fiber material, a polyester material, a polyolefin polymer material, and / or a combination of the aforementioned materials. Preferably, the secondary nonwoven fiber backing comprises a veil-shaped nonwoven fiberglass material. The organic binder, when present, is typically present in an amount between 1% and 10% by weight based on the total weight of the second nonwoven fiber backing. In general, the secondary nonwoven fiber material will have a weight or surface density slightly higher than that of the primary nonwoven fiber layer. In a preferred embodiment, the secondary nonwoven fiber has a weight per unit area in the range of 20 g / m² to 100 g / m², more preferably in the range of 30 g / m² to 80 g / m², and more preferably in the range of 30 g / m² to 60 g / m².Suitable non-woven glass veils, mats, or fleeces are commercially available under the trade name Evalith® from Johns Manville, Denver, Colorado, USA, which include, but are not limited to, Evalith® ST-3022, S 4030, and S 5030, and under the trade name Changhai® from Taishan Fiberglass Inc., Economic Development Zone, Taian, Shandong, P.R. China, which includes, but are not limited to, Changhai® S-SM30, S-SM50, S-HM30, and S-HM50. The presence of the second nonwoven fiber material helps prevent the fiber reinforcement material in the structural reinforcement layer from showing through on the surface of the molded material after curing. It also ensures that sufficient resin composition is retained within the surface enhancement layer during curing, preventing the formation of narrow grooves or other surface irregularities due to insufficient resin. Like the first nonwoven fiber material, the second nonwoven fiber material can also prevent air entrapment or help dissipate trapped air. In one particular aspect of the present invention, the molding material does not comprise any reinforcing material, and the molding material, therefore, essentially consists of the primary non-woven fiber layer, the secondary non-woven fiber layer, and the resin layer. In the embodiments of the invention according to the first aspect in which there is no reinforcement, the total resin content of the molding material may be contained in the resin associated with the nonwoven primary layer. The preferred total resin content of the molding materials in this embodiment will depend on the intended use of the molding material, but preferably the resin content of the molding material is in the range of 40% to 75% by weight of the molding material, more preferably between 50% and 60% by weight of the molding material. In a second aspect of the present invention, the molding materials comprise a reinforcing layer. The secondary nonwoven fiber layer is located between the primary nonwoven fiber layer and the reinforcing layer. The presence of this reinforcing layer helps improve the structural integrity of the molding materials, thus facilitating storage, transport, and handling. ηζηαηη / ζζηζ / Ε / γίΛΐ Preferably, the secondary nonwoven fiber layer is sewn to the surface of the reinforcing layer. The layer can be sewn with a polyester yarn having a tex value in the range of 5 dtex to 90 dtex, preferably between 40 dtex and 85 dtex, and more preferably between 70 dtex and 85 dtex. The structural reinforcement layer can take many forms. Normally, the molding material according to the second aspect of the present invention will contain several layers of structural reinforcement, although for some applications a single layer may be sufficient. The fibrous reinforcement material may be in the form of a continuous sheet or mat, or continuous filaments. In other embodiments, the fibrous reinforcement material comprises short-length fibers, for example, a chopped-strand mat. The fibrous reinforcement material may be in the form of multiple fiber tows, each containing multiple fiber filaments. The tows may be sewn or woven to form a fabric. The fibers may consist of natural materials, such as cotton, linen, hemp, wool, or silk; or semi-synthetic materials, such as rayon, viscose, modal, etc.; or synthetic materials, such as carbon, polyester, mineral fibers, nylon, acrylic, glass, aramid (aromatic polyamide), etc. In preferred embodiments, the fiber reinforcement comprises carbon fibers or glass fibers. In some embodiments, the fibrous reinforcement material is in the form of a woven fabric. In other embodiments, the fibrous reinforcement material comprises a unidirectional (UD) fabric in which the majority of the fibers, strands, or tow present in the fabric run in a single direction, although a small number of fibers, strands, or tow may run in a direction different from the majority, for example, as cross-stitches to maintain the unidirectional alignment of the latter. The fibers, strands, or tow of a unidirectional fabric may be kept aligned by various methods, including weaving, sewing, and bonding. Accordingly, such unidirectional fabrics may be woven or nonwoven. In other embodiments, the fibrous reinforcement material comprises a unidirectional fabric in combination with a biaxial or multiaxial fabric or mat, where either component may be woven or nonwoven. Woven and nonwoven fabrics suitable for use in composite materials are commercially available from specialist manufacturers, including but not limited to Chomarat Textiles Industries, Esher, Surrey, UK; Hexcel Reinforcements UK Limited, Narborough, Leicestershire, UK; and Zhenshi Group Hengshi Fibreglass Fabrics Co., Ltd., Tongxiang Economic Development Zone, Jiaxing, Zhejiang, 314500 China. In one embodiment, the woven or nonwoven fabric is a carbon fiber or glass fiber fabric, such as BB200, BB600, or BB1200, where the designation BB1200, for example, refers to a biaxial glass fabric having a unit weight of 1200 g / m². Hybrid or mixed fiber systems may also be provided for. The use of cracked (i.e., stretchable) or selectively discontinuous fibers may be advantageous for facilitating the layering of the molding material according to the present invention and improving its formability. The weight per unit area of ​​the fibrous reinforcing material is generally between 40 g / m2 and 4000 g / m2. In preferred embodiments, the weight per unit area of ​​the fibers is preferably in the range between 100 g / m2 and 2500 g / m2, more preferably between 150 g / m2 and 2000 g / m2. The fibrous reinforcement material in the structural reinforcement layer, or layers where more than one layer is present, will generally be a heavy, non-crimp fabric, such as fiberglass. For fiberglass reinforcements, fibers between 68 tex and 2400 tex (grams per kilometer of yarn) are specially suited. In particular embodiments of the second aspect of the present invention, the reinforcing layer may comprise at least two layers, each of which contains unidirectional fibers. The unidirectional fibers of each layer may be oriented in different directions. In one embodiment, the unidirectional fiber layers and the secondary non-woven fiber layer are sewn together, optionally using the same stitch thread. The reinforcing layer preferably comprises a fibrous reinforcing material and a formulated reinforcing resin matrix, and in preferred embodiments the formulated reinforcing resin matrix has the same composition as the resin of the resin layer. In the embodiments of the invention according to the second aspect, in which a reinforcing layer exists, the total resin content of the molding material may be contained in the resin associated with the primary nonwoven layer, or the resin may be distributed throughout the material, either as a number of discrete layers along the length of the material or as a single matrix. The preferred total resin content of the molding materials in this embodiment will depend on the intended use of the molding material and also on the weight of the reinforcing material, but preferably the resin content of the molding material is in the range of 5% to 60% by weight based on the weight of the molding material.For example, in molding materials intended for use in infusion systems, the total resin content is preferably between 5% by weight and 50% by weight, more preferably between 5% by weight and 20% by weight based on the weight of the molding material. Similarly, for molding materials intended for use in combination with at least partially pre-impregnated materials without infusion, the total resin content is preferably between 20% by weight and 60% by weight, more preferably between 25% by weight and 50% by weight based on the weight of the molding material. The present invention further provides for the use of the molding material of the present invention in combination with one or more layers of pre-impregnated fibrous reinforcement to form a laminated structure, the pre-impregnated layer having a resin content in the range of 30% to 45% based on the weight of the pre-impregnated material. The present invention further provides for the use of the molding material of the present invention in combination with one or more resin-free (dry) layers of fibrous reinforcement to form a laminated structure in a resin infusion process. The present invention also provides a method for manufacturing a laminated structure, the method consisting of placing a molding material according to the present invention on the surface of a mold or tool with the resin layer exposed on the second surface of the primary non-woven fiber layer in contact with the tool or mold surface; apply one or more layers of resin-free (dry) fibrous reinforcement to the opposite surface of the molding material to form a stack; infuse the pile with an infusion resin, and cure the infused pile. In the method of manufacturing a laminated structure of the present invention, the molding material used in the method may be a molding material according to the first aspect of the present invention, i.e., a molding material not comprising a reinforcing layer. Alternatively, the molding material may be a molding material of the second aspect of the present invention, i.e., a molding material comprising a reinforcing layer, and in particular a molding material comprising a reinforcing layer and wherein the resin content of the molding material is in the range of 5% by weight to 50% by weight, preferably in the range of 5% by weight to 20% by weight, based on the weight of the molding material. In the method of manufacturing a laminated structure according to the present invention, at least one layer of pre-impregnated fibrous reinforcement can be included in the stack before infusion with the resin. In the method of manufacturing a laminated structure according to the present invention, any conventional infusion process and infusion resins can be used, depending on the intended use of the laminated structure. Brief description of the drawings The invention will now be described by way of example only with reference to the accompanying drawings. Figure 1 presents a schematic view of a molding material according to an embodiment of the present invention; Figure 2 presents a schematic view of another molding material according to another embodiment of the invention. Figure 1 shows a molding material 100 comprising a primary nonwoven fiber layer 102 and a secondary nonwoven fiber layer 104. The primary nonwoven fiber layer 102 contains a resin layer 106 that is exposed on its surface, but extends along the length of the primary nonwoven fiber layer 102 and at least comes into contact with, and optionally partially or completely extends into, the secondary nonwoven fiber layer 104. The primary and secondary nonwoven fiber layers 102, 104 are bonded together by the adhesiveness of the resin layer 106. In one particular embodiment, the primary nonwoven layer 102 is a thermoplastic nonwoven veil containing a mixture of polyamide and polyester material with a weight of 15 g / m2; the resin layer 106 has a weight of 65 g / m2, and the secondary nonwoven fiber layer 104 is a fleece of fiberglass material with a weight of 50 g / m2. In a common use, the molding material 100 is in contact with a mold surface, with the top surface of the resin layer 106 in contact with the mold. Additional resin-pre-impregnated reinforcing layers, at least partially, may be located on top of the molding material 100, i.e., in contact with the non-woven secondary layer 104, to construct a composite layer that is then cured to produce a composite part. In an alternative use, the molding material 100 is in contact with a tool surface, with the top surface of the resin layer 106 in contact with the tool.Additional non-impregnated (i.e., dry) reinforcing layers can be placed on top of the molding material 100, i.e., in contact with the non-woven secondary layer 104 to build a composite layer that is then infused with resin and cured to produce a composite part. Figure 2 shows a molding material 200 comprising a primary nonwoven fiber layer 202 and a secondary nonwoven fiber layer 204. The primary nonwoven fiber layer 202 contains a resin layer 206 that is exposed on its surface and extends the length of the primary nonwoven fiber layer 202 and at least in contact with, and optionally partially or fully extends into, the secondary nonwoven fiber layer 204. A fibrous reinforcing layer 208 is located on the opposite surface of the secondary nonwoven fiber layer 204. The primary and secondary nonwoven fiber layers 202 and 204 are bonded by the adhesiveness of the resin layer 206, and the secondary nonwoven fiber layer 204 and the reinforcing layer 208 are joined by seams. This allows the reinforcing layer 208 to remain unimpregnated with resin (dry). In one particular embodiment, the resin composition contains a difunctional epoxy in combination with a urea-based curing agent; the primary nonwoven fiber layer 202 is a nonwoven polyester veil weighing 15 g / m2; the resin layer 206 weighs 140 g / m2, and the secondary nonwoven fiber layer 204 is a fiberglass fleece weighing 50 g / m2. In a preferred embodiment, the 208 reinforcement layer is preferably in the form of two unidirectional fiber layers combined to form a biaxial layer, preferably with a + / -45 degree orientation. In typical use, molding material 200 is in contact with a mold surface, with the top surface of resin layer 206 in contact with the mold. Additional reinforcing layers are placed on top of molding material 200 to create a composite layer, which is then cured to produce a composite part. In an alternative use, molding material 200 is in contact with a tooling surface, with the top surface of resin layer 206 in contact with the tooling. Additional non-impregnated (i.e., dry) reinforcing layers can be placed on top of molding material 200, i.e., in contact with the non-woven secondary layer 204, to create a composite layer that is then infused with resin and cured to produce a composite part. Therefore, a molding material is provided that can be used in combination with pre-impregnated fibrous reinforcement layers having a resin content in the range of 30% by weight to 45% by weight based on the weight of the pre-impregnated material, and that can also be used in combination with non-impregnated fibrous reinforcement layers to form a laminate in an infusion system. Examples Example 1 A resin composition (composition 1) was formulated from: ηζηαηη / ζζηζ / Ε / γίΛΐ 72.9 g Kukdo KFR136SL (a semi-solid bisphenol A diglycidyl ether epoxy resin manufactured by Kukdo Chemical Company Limited, Seoul, Korea); 18.2 g Epikote®828 (a bisphenol A diglycidyl ether liquid epoxy resin manufactured by Hexion Inc., Columbus, Ohio, United States); 2.9 g of Dyhard® UR500 (a dual-functional latent urone accelerator in powder form manufactured by Alzchem Group AG, Trostberg, Germany). The components were thoroughly mixed at a temperature between 50°C and 60°C until the mixture was uniform in consistency. A molding material was constructed that has the following architecture: (1) a layer of Evalith® S 5030 (a fiberglass fleece with a weight per unit area of ​​50 g / m2 manufactured by Johns Manville, Denver, Colorado, United States); (2) a layer of lightweight, fully synthetic non-woven fiber veil comprising a mixture of polyester and polyamide fibers with a unit weight of 15 g / m2 (manufactured by Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom); and (3) a 65 g / m2 layer of resin composition 1. The assembled layers were consolidated by passing through an S-shaped wrapping roller system heated to 80°C, into a molding material corresponding to molding material 100 shown in Figure 1. A composite part was produced by placing molding material 100 into a composite tool treated with Zyvax® Watershield™ (a water-soluble, silicone-free release agent manufactured by Freeman Manufacturing and Supply Company, Avon, Ohio, USA), followed by 3 layers of BB1000 fabric (1000 g / m2 biaxial non-crimp glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, UK) and 1 layer of Bleeder Lease B (62 g / m2 silicone-treated nylon fabric from Airtech Europe Sari, Differdange, Luxembourg) and infused with Hexion RIM R135 / RIM H 137 (a combination of liquid epoxy resin and hardener from Hexion Inc., Columbus, Ohio, USA) before curing at 80 °C for 6 hours at a pressure of 100,000 Pa (1 bar). Once cooled, the cured molded part was removed for further inspection and testing. Example 2 A resin composition (composition 2) was formulated from the same components in the same quantities as composition 1, but with the addition of 6 g of Aerosil® R202 (a hydrophobic pyrogenic silica rheology modifier manufactured by Evonik Resource Efficiency GmbH, Hanau-Wolfgang, Germany). The components were thoroughly mixed at a temperature between 50°C and 60°C until the mixture was uniform in consistency. A molding material was constructed that has the following architecture: (1) a layer of LBB1200 fabric (1250 g / m2 non-crimp triaxial glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom); (2) a layer of Evalith® S 5030 (a fiberglass fleece with a weight per unit area of ​​50 g / m2 manufactured by Johns Manville, Denver, Colorado, United States); (3) a layer of lightweight, fully synthetic non-woven fiber veil comprising a mixture of polyester and polyamide fibers with a unit weight of 15 g / m2 (manufactured by Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom); and (4) a 140 g / m2 layer of resin composition 2. The assembled layers were consolidated by passing through an S-shaped wrapping roller system heated to 80°C, into a molding material corresponding to molding material 200 shown in Figure 2. A composite part was produced by placing molding material 1 into a composite tool treated with Zyvax® Watershield™ (a water-soluble, silicone-free release agent manufactured by Freeman Manufacturing and Supply Company, Avon, Ohio, USA), followed by 3 layers of BB1000 fabric (1000 g / m2 biaxial non-crimp glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, UK) and 1 layer of Bleeder Lease B (62 g / m2 silicone-treated nylon fabric from Airtech Europe Sari, Differdange, Luxembourg) and infused with Hexion RIM R135 / RIM H 137 (a combination of liquid epoxy resin and hardener from Hexion Inc., Columbus, Ohio, USA) before curing at 80 °C for 6 hours at a pressure of 100,000 Pa (1 bar). Once cooled, the cured molded part was removed for further inspection and testing. Example 3 Resin composition 2 was used to form a molding material having the following architecture: (1) a 400 g / m2 layer of resin composition 2; (1) a layer of LBB1200 fabric (1250 g / m2 non-crimp triaxial glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom); (3) a layer of Evalith® S 5030 (a fiberglass fleece with a weight per unit area of ​​50 g / m2 manufactured by Johns Manville, Denver, Colorado, United States); (4) a layer of lightweight, fully synthetic non-woven fiber veil comprising a mixture of polyester and polyamide fibers with a unit weight of 15 g / m2 (manufactured by Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom); and (5) a 400 g / m2 layer of resin composition 2. The assembled layers were consolidated by passing through an S-shaped wrapping roller system heated to 80°C, into a molding material corresponding to molding material 200 shown in Figure 2. Molding material 200 was placed in a composite tool treated with Zyvax® Watershield™ (a water-soluble, silicone-free release agent manufactured by Freeman Manufacturing and Supply Company, Avon, Ohio, USA) with the resin composition layer (5) adjacent to the mold face. Two layers of HexPly® 79 (a prepreg manufactured by Hexcel GmbH, Neumarkt, Germany) were placed over the molding material in the mold, i.e., adjacent to the resin layer (1); and the assembly was vacuum-cured for 6 hours at 80°C and 100,000 Pa (1 bar) pressure. Upon cooling, the cured molded part was removed for inspection and further testing.

Claims

1. A molding material comprising: a) a primary nonwoven fiber layer; b) a secondary nonwoven fiber layer, and c) a resin layer; wherein the resin layer bonds the secondary nonwoven fiber layer to a first surface of the primary nonwoven fiber layer, and the resin layer is exposed on the second surface of the primary nonwoven layer.

2. The molding material according to claim 1, wherein the secondary non-woven fiber layer is at least partially impregnated, and optionally fully impregnated, with the resin of the resin layer.

3. The molding material according to claim 1 or 2, wherein the resin layer comprises a formulated resin matrix comprising at least one resin component, at least one curing agent, and optionally a filler.

4. The molding material according to claim 3, wherein the formulated resin matrix comprises at least one multifunctional bisphenol epoxy resin material in combination with a urea-based curing agent.

5. The molding material according to claim 3 or 4, wherein the formulated resin matrix comprises between 1% by weight and 10% by weight of a filler based on the weight of the formulated resin matrix, preferably a silica filler or an organophilic phyllosilicate.

6. The molding material according to any of the preceding claims, wherein the primary nonwoven fiber layer comprises a polyester or an aliphatic or semi-aromatic polyamide fiber material, preferably having a weight per unit area in the range of 1 g / m2 to 80 g / m2, more preferably between 5 g / m2 and 50 g / m2, even more preferably between 10 g / m2 and 40 g / m2.

7. The molding material according to any of the preceding claims, wherein the secondary nonwoven fiber layer comprises a fiberglass material, or a polyester material, or a polyolefin polymeric material and / or a combination of the aforementioned materials, preferably having a weight per unit area greater than the weight per unit area of ​​the primary nonwoven fiber layer, more preferably having a weight per unit area in the range of 20 g / m2 to 100 g / m2, even more preferably in the range of 30 g / m2 to 80 g / m2, and most preferably in the range of 30 g / m2 to 60 g / m2.

8. The molding material according to any of the preceding claims, consisting essentially of the primary non-woven fiber layer, the secondary non-woven fiber layer, and the resin layer.

9. The molding material according to claim 8, wherein the resin content of the molding material is in the range of 40% by weight to 75% by weight based on the weight of the molding material, preferably between 50% by weight and 60% by weight based on the weight of the molding material.

10. The molding material according to any of claims 1 to 7, wherein the molding material comprises a reinforcing layer, the secondary nonwoven fiber layer being located between the primary nonwoven fiber layer and the reinforcing layer.

11. The molding material according to claim 10, wherein the secondary layer of non-woven fiber is sewn to the surface of the reinforcing layer.

12. The molding material according to claim 10 or 11, wherein the reinforcing layer comprises at least two layers, each layer containing unidirectional fibers.

13. The molding material according to claim 12, wherein the unidirectional fibers of each layer are in different directions.

14. The molding material according to claim 12 or 13, wherein the unidirectional fiber layers and the secondary non-woven fiber layer are joined by stitching.

15. The molding material according to any of claims 10 to 14, wherein the reinforcing layer comprises a fibrous reinforcing material and a formulated reinforcing resin matrix.

16. The molding material according to claim 15, wherein the formulated reinforcing resin matrix has the same composition as the resin of the resin layer.

17. The molding material according to any of claims 10 to 16, wherein the resin content of the molding material is in the range of 5% by weight to 60% by weight based on the weight of the molding material, preferably between 5% by weight and 50% by weight, more preferably between 5% by weight and 20% by weight based on the weight of the molding material, or between 20% by weight and 60% by weight, more preferably between 25% by weight and 50% by weight based on the weight of the molding material.

18. Use of the molding material according to any of claims 1 to 17 in combination with one or more layers of pre-impregnated fibrous reinforcement to form a laminated structure, the pre-impregnated layer having a resin content in the range of 30% by weight to 45% by weight based on the weight of the pre-impregnated material.

19. Use of the molding material according to any of claims 1 to 17, in combination with one or more layers of resin-free (dry) fibrous reinforcement to form a laminated structure in a resin infusion process.

20. A method of manufacturing a laminated structure, the method comprising placing a molding material according to any of claims 1 to 17 on the surface of a mold or tool with the resin layer exposed on the second surface of the primary nonwoven fiber layer in contact with the tool or mold surface; applying one or more resin-free (dry) fibrous reinforcement layers to the opposite surface of the molding material to form a stack; infusing the stack with an infusion resin, and curing the infused stack.

21. The method according to claim 20, wherein the molding material is a material